Truncation of the gp41 construct just past its transmembrane domain, leaving residues 1-190, results in a well-structured protein, soluble in dodecylmaltoside while adopting its natural homo-trimeric form. The protein is found to be quite stable, even at temperatures of 50C, and samples are found to be suitable for NMR spectroscopy. Preliminary analysis shows that even thought the ecto-domain resonances are severely broadened, characteristic of slow molecular tumbling, the fusion domains of the trimer yield good NMR spectral characteristics. We find that these fusion domains exhibit chemical shifts that fall very close to those of the isolated domain, previously studied in SDS micelles and found to be uniformly alpha-helical. The fusion domains exhibit effective correlation times that are much shorter than for the remainder of the large trimeric complex, indicating that the intact fusion domain helices are highly mobile within the detergent micelle, while retaining their helical conformation. This excludes the previously hypothesized interaction with the gp41 transmembrane domain.